#include <stdio.h>
#define N 20
typedef struct
{
    char no[10];
    double score;
} RECORD;

double avg(RECORD x[], int n);

int main()
{
    RECORD a[N];
    int n, i;
    double av;
    scanf("%d", &n);
    for (i = 0; i < n; i++)
        scanf("%s%lf", a[i].no, &a[i].score);
    av = avg(a, n);
    printf("%f", av);
    return 0;
}

/* 请在这里填写答案 */
double avg(RECORD x[], int n)
{
    double sum = 0.0;
    for (int i = 0; i < n; i++)
        sum += x[i].score;
    return sum / n;
};
